Effects of obesity and hypertension on ventricular myocytes: comparison of cells from adult SHHF/Mcc-cp and JCR:LA-cp rats

Objective: The aim was to compare β adrenergic receptors, cAMP production, and Ca2+ accumulation by the sarcoplasmic reticulum in ventricular cardiomyocytes from female SHHF/Mcc- cp and JCR:LA- cp rats. Whereas rats from both strains exhibit gross obesity when the animals are homozygous for the recessive “corpulent” gene, the SHHF rats, which are hypertensive, all develop heart failure during their second year of life. The normotensive JCR:LA- cp animals do not. Methods: β Adrenergic receptor number, ligand affinity, isoprenaline and forskolin stimulated cyclic AMP production, and ATP dependent, phosphate supported 45Ca2+ uptake by the sarcoplasmic reticulum were compared in ventricular cardiomyocytes isolated from 6 month old obese female SHHF/Mcc- cp and obese and lean female JCR:LA-cp rats. Results: Bmax and Kd for (–)-[125iodo]-cyanopindolol (l25ICYP) binding were each –50% lower in SHHF/Mcc- cp v JCR:LA- cp myocytes. Cyclic AMP production in response to isoprenaline, isoprenaline plus isobutylmethylxanfhine (IBMX), and forskolin pjus IBMX was also significantly depressed in the SHHF/Mcc- cp cells. In addition, sarcoplasmic reticular 45Ca2+ uptake by SHHF/ Mcc- cp cells was 35% lower than in lean or obese JCR:LA- cp myocytes. Isoprenaline stimulated cAMP production and sarcoplasmic reticular Ca2+ uptake by the lean JCR:LA-cp cells were comparable to that described previously for myocytes from normal Sprague-Dawley rats. By contrast, Bmax and Kd for 125ICYP binding by the JCR myocytes differed substantially from previously described results for normal Sprague-Dawley rats, whereas values for the SHHF cells did not. Conclusions: Declines in Ca sequestration by the sarcoplasmic reticulum of ventricular cardiomyocytes from obese, hypertensive SHHF rats are not related to their obesity. However, obesity may contribute to the decline in cAMP production. This may account, in part, for the exacerbation by obesity of cardiac dysfunction in essential hypertension. Cardiovascular Research 1993; 27 :238-242